A NEW PHYTOSAUR FROM THE TRIAS OF ARIZONA 



15s 



The following table comparing the two forms will show the chief 

 differences on which the new species is established. 



Machaeroprosopus andersoni 

 Postero-median border of supra- 

 temporal fenestrae not completely- 

 depressed. 



Anterior border of nares not elevated. 



Machaeroprosoptis validus 

 Postero-median border of supra- 

 temporal fenestrae completely 

 depressed. 



Anterior border of nares elevated 

 above lateral borders. 



Terminal 

 abrupt. 



expansion of rostrum 



Terminal 

 gradual. 



expansion of rostrum 



Nasals not extending to anterior 

 border of nares. 



Greatest length of maxillae above 

 alveolar margin. 



Approximately seventy-four teeth in 

 upper dentition. 



Six large teeth in terminal expansion 

 of rostrum. 



Alveolae crowded, occasionally con- 

 fluent. 



No lateral expansion of rostrum at 

 posterior end of premaxillae. 



Nasals extending some distance in 

 front of anterior border of nares. 



Greatest length of maxillae at alveolar 

 margin. 



Approximately ninety-four teeth in 

 upper dentition. 



Four large teeth in terminal expansion 

 of rostrum. 



Alveolae not crowded. 



Lateral expansion of rostrum at 

 posterior end of premaxillae. 



The Phytosauria are a unified group in that they all tend to de- 

 velop certain pecuHarities that set them off from other groups in a 

 striking manner. All developed the snoutlike elongation of the 

 skull, an elongation that left the nares far from the tip. In some 

 cases there seems to have been an actual retreat of the nares. 

 There seems also to have been a tendency to elevate the nares 

 above the plane of the cranium proper, a goal very conspicuously 

 reached in several forms. All of the phytosaurs showed a more 

 or less marked development of greatly enlarged terminal teeth 

 and most of them developed at least a crude slicing dentition 

 farther back in the jaws. 



These modifications or tendencies are so distinctive that they 

 have called forth considerable speculation as to the habits of the 



